How do plants perceive the world?

Plants perceive the world without eyes, ears or brains. Understanding how can teach us a lot about them, and potentially a lot about us as well.

Plants, according to Jack C Schultz, “are just very slow animals”.

This is not a misunderstanding of basic biology. Schultz is a professor in the Division of Plant Sciences at the University of Missouri in Columbia, and has spent four decades investigating the interactions between plants and insects. He knows his stuff.

Instead, he is making a point about common perceptions of our leafy cousins, which he feels are too often dismissed as part of the furniture. Plants fight for territory, seek out food, evade predators and trap prey. They are as alive as any animal, and – like animals – they exhibit behaviour.

“To see this, you just need to make a fast movie of a growing plant – then it will behave like an animal,” enthuses Olivier Hamant, a plant scientist at the University of Lyon, France. Indeed, a time-lapse camera reveals the alien world of plant behaviour in all its glory, as anyone who has seen the famous woodland sequence from David Attenborough’s Life series can attest.

These plants are moving with purpose, which means they must be aware of what is going on around them. “To respond correctly, plants also need sophisticated sensing devices tuned to varying conditions,” says Schultz.

So what is plant sense? Well, if you believe Daniel Chamovitz of Tel Aviv University in Israel, it is not quite so different from our own as you might expect.

When Chamovitz set out to write his 2012 book What a Plant Knows – in which he explores how plants experience the world by way of the most rigorous and up-to-date scientific research – he did so with some trepidation.

“I was incredibly wary about what the response would be,” he says. A Beethoven symphony is of little consequence to a plant, but the approach of a hungry caterpillar is another story

His worry was not unfounded. The descriptions in his book of plants seeing, smelling, feeling and, indeed, knowing have echoes of The Secret Life of Plants, a popular book published in 1973 that appealed to a generation raised on flower power, but contained little in the way of facts.

The earlier book’s most enduring claim, perhaps, is the thoroughly discredited idea that plants respond positively to the sound of classical music.